Add Windows Explorer context menu integration

- Add context menu entries for all supported file types
- Implement CLI interface with --convert and --convert-to commands
- Create installation/uninstallation scripts (registry, PowerShell, batch)
- Add NSIS installer integration for automatic context menu setup
- Support direct conversion from right-click menu
- Include comprehensive documentation and usage instructions

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -45,6 +45,7 @@
     "files": [
       "src/**/*",
       "assets/**/*",
+      "scripts/**/*",
       "node_modules/**/*",
       "package.json"
     ],
@@ -72,6 +73,14 @@
       "target": "nsis",
       "icon": "assets/icon.ico"
     },
+    "nsis": {
+      "oneClick": false,
+      "allowToChangeInstallationDirectory": true,
+      "createDesktopShortcut": true,
+      "createStartMenuShortcut": true,
+      "shortcutName": "PanConverter",
+      "include": "scripts/nsis-installer.nsh"
+    },
     "linux": {
       "target": [
         "deb",